Re: [PATCH v9 15/20] ref-filter: modify the 'lstrip=<N>' option to work with negative '<N>'

From: Karthik Nayak <karthik.188@gmail.com>
Date: Dec 28, 2016, 08:54 UTC
Message-ID: <CAOLa=ZTs7G_fk77j-QxiM7fLncPRtJ8DfNGaw1upyT1CSx3Xyw@mail.gmail.com>
In-Reply-To: <xmqqo9zx6phw.fsf@gitster.mtv.corp.google.com>

On Wed, Dec 28, 2016 at 2:41 AM, Junio C Hamano <gitster@pobox.com> wrote:

Show 18 quoted lines

> Karthik Nayak <karthik.188@gmail.com> writes:
>
>> Currently the 'lstrip=<N>' option only takes a positive value '<N>'
>> and strips '<N>' slash-separated path components from the left. Modify
>> the 'lstrip' option to also take a negative number '<N>' which would
>> only _leave_ behind 'N' slash-separated path components from the left.
>
> "would only leave behind N components from the left" sounds as if
> the result is A/B, when you are given A/B/C/D/E and asked to
> lstrip:-2.  Given these two tests added by the patch ...
>
>> +test_atom head refname:lstrip=-1 master
>> +test_atom head refname:lstrip=-2 heads/master
>
> ... I somehow think that is not what you wanted to say.  Instead,
> you strip from the left as many as necessary and leave -N
> components that appear at the right-most end, no?
>

Yup, you're correct it should be 'leave -N components from the right-most end'. Will change that.

Show 16 quoted lines

>> --- a/Documentation/git-for-each-ref.txt
>> +++ b/Documentation/git-for-each-ref.txt
>> @@ -98,7 +98,8 @@ refname::
>>       abbreviation mode. If `lstrip=<N>` is appended, strips `<N>`
>>       slash-separated path components from the front of the refname
>>       (e.g., `%(refname:lstrip=2)` turns `refs/tags/foo` into `foo`.
>> -     `<N>` must be a positive integer.
>> +     if `<N>` is a negative number, then only `<N>` path components
>> +     are left behind.
>
> I think positive <N> is so obvious not to require an example but it
> is good that you have one.  The negative <N> case needs illustration
> more than the positive case.  Perhaps something like:
>
>     (e.g. %(refname:lstrip=-1) strips components of refs/tags/frotz
>     from the left to leave only one component, i.e. 'frotz').

Good point, but i'll be using N = -2 rather than -1 since N=-1 can also be obtained by using N=2 as shown in the existing documentation. With N=-2 we differentiate the use cases of N= positive and negative numbers.

diff --git a/Documentation/git-for-each-ref.txt
b/Documentation/git-for-each-ref.txt
index 9123c6f..814d77a 100644
--- a/Documentation/git-for-each-ref.txt
+++ b/Documentation/git-for-each-ref.txt
@@ -99,7 +99,8 @@ refname::
        slash-separated path components from the front of the refname
        (e.g., `%(refname:lstrip=2)` turns `refs/tags/foo` into `foo`.
        if `<N>` is a negative number, then only `<N>` path components
-       are left behind.
+       are left behind. (e.g., `%(refname:lstrip=-2)` turns
+       `refs/tags/foo` into `tags/foo`).


>
> Would %(refname:lstrip=-4) attempt to strip components of
> refs/tags/frotz from the left to leave only four components, and
> because the original does not have that many components, it ends
> with refs/tags/frotz?
>

It ends up with 'refs/tags/frotz' since there are not enough components.

> I am debating myself if we need something like "When the ref does
> not have enough components, the result becomes an empty string if
> stripping with positive <N>, or it becomes the full refname if
> stripping with negative <N>.  Neither is an error." is necessary
> here.  Or is it too obvious?

I had the same self-debate, and dropped it for being too obvious.

On Wed, Dec 28, 2016 at 8:38 AM, Jacob Keller <jacob.keller@gmail.com> wrote:
>
> I do not think it hurts to have, and makes this obvious.
>

But as Jacob mentioned, it doesn't hurt to mention the obvious
sometimes. So i'll
add that in :)

-- 
Regards,
Karthik Nayak